Bone is a metabolically active and highly organized tissue. Bone contains two distinct cell types, the osteoblasts or bone forming cells and the osteoclasts, or bone resorbing cells. Bone remodeling is a normal process that involves the resorption of bone by osteoclasts and the synthesis of bone matrix by osteoblasts. These two processes are normally integrated to maintain both the structural integrity of the skeletal system and homeostasis of bone. Both these processes are influenced by a wide variety of systemic and local factors. An imbalance of osteoblast and osteoclast functions can arise from variety of hormonal changes or perturbations of inflammatory and growth factors resulting in skeletal abnormalities characterized by increased or decreased bone mass. This may lead to excessive bone loss and eventually fracture.
Osteoclasts are specialized monocyte/macrophage family members that differentiate from hemopoietic precursors. Increased osteoclast activity is seen in osteoporosis (Gross et al., 1996), rheumatoid arthritis (Seitz and Hunstein, 1985), Paget's disease (Siris, 1999), and many other diseases of clinical importance. In these disorders bone resorption exceeds bone formation, resulting in decreased skeletal mass. This causes bones to become thin, fragile and susceptible to fracture. The consequences of osteoporotic bone fractures include chronic pain in bone, body deformity including height loss and muscle weakness.
Osteoporosis is now a serious problem that imposes substantial limitations on the affected individuals. In humans, 1 in 3 women and 1 in 12 men over 45 years are at risk of suffering painful and deforming fractures as a result of osteoporosis. More women die after hip fractures than from cancers of ovaries, cervix and uterus. Osteoporosis occurs at an earlier age in Indian males and females compared to western countries (Gupta, 1996).
Most bone diseases occur due to increased osteoclast activity and increased bone resorption. Bone resorption and loss of calcium from bone are complications associated with arthritis, many cancers and with bone metastases of breast and prostate tumors. Current treatment for these diseases primarily targets osteoclasts.
Drugs that inhibit the formation or activity of osteoclasts are valuable for treating these diseases. However, a variety of disadvantages are associated with current therapeutic agents (such as estrogen and selective estrogen receptor modulators, bisphosphonates and calcitonin) used in osteoporosis and other metabolic bone disorders (Rodan and Martin, 2000). Drugs developed for treating osteoporosis and related disorders showed adverse events and contraindications (Watts, 1999). The side effects of current therapies include increase in the risk of breast and uterine cancers, upper gastrointestinal distress and induction of immune responses.
Drugs that inhibit the formation or activity of osteoclasts and with no toxicity and harmful side effects will be valuable for treating osteoporosis, Paget's disease, and inflammation of bone associated with rheumatoid arthritis or periodontal disease.
Natural products from plants and organisms have frequently been used as a source for development of effective drugs. There is an increased interest in analysis of natural products from marine organisms. Sea animals contain metabolites which can be used for treatment of many diseases.
An extract from mussels was first shown to have the anti-inflammatory activity in rats (Miller and Ormrod, 1980). In these studies, a preparation from New Zealand green mussel (Perna canaliculus) effectively reduced the rat paw edema but only if injected into the peritoneal cavity. Freeze-dried extract preparations from mussels have been used as anti-inflammatory treatments (Caughey et al., 1983). A preliminary report on the use of mussel hydrolysate obtained from mussel meat by acid hydrolysis indicated that the hydrolysate had virus-inhibiting activity against influenza viruses (Bichurina et al., 1994).
The extract prepared from the Indian green mussel (Perna viridis) has previously been found to be active against all influenza, herpes and hepatitis viral strains. The extract is also found to possess not only prophylactic efficacy for protection from several viral diseases but it also shows a high therapeutic property against these diseases.
A process for extracting mussel hydrolysate is disclosed in an unpublished, pending, process patent application filed by the National Institute of Oceanography, Goa, India (Patent No. 493/DEL/99) on Mar. 31, 1999.
In the present invention, an attempt has been made to study the effect of extract prepared from the Indian green mussel on osteoclast differentiation and bone resorption in vitro.